Diabetes and cancer are major causes of illness and death worldwide. The CDC has released a report showing that the prevalence of diabetes has increased to 25.8 million in America, or 8.3% of the national population. It’s estimated that 2.5 million of these individuals are survivors of breast cancer. Research has shown that diabetes increases the risk of breast cancer. Furthermore, two of the major risk factors for type 2 diabetes—older age and obesity—have also been associated with breast cancer. A concern for physicians managing patients who have diabetes and are diagnosed with breast cancer is that care for the preexisting diabetes often goes on the back burner; the breast cancer takes center stage. Patients may sometimes view their breast cancer diagnosis as a greater threat to their lives than their diabetes.

Alarming Data on Breast Cancer-Diabetes Relationship

In order to better understand the relationship between breast cancer and diabetes, my colleagues and I conducted a systematic review and meta-analysis of previous research. Published in the January 2011Journal of Clinical Oncology, our investigation looked in depth at eight studies involving patients with preexisting diabetes and breast cancer outcomes. Six of the studies reported a risk estimate effect on all-cause mortality in patients with breast cancer. We then qualitatively summarized other prognostic outcomes. When compared with those who did not have diabetes, women with breast cancer and preexisting diabetes had a 49% greater risk of death.

“When compared with those who did not have diabetes,
women with breast cancer and preexisting diabetes had a
49% greater risk of death.”

Another important finding from our research was that three of four studies found preexisting diabetes to be associated with more advanced-stage breast cancer when patients presented to their healthcare provider. Additionally, women with breast cancer and preexisting diabetes tended to receive altered regimens for breast cancer treatment and experienced increased toxicity from chemotherapy. In many cases, the altered regimens were potentially less effective treatments than what would typically be administered.

Treating Breast Cancer in Diabetics

Considering that diabetes is a systemic disease with many different effects on the body, healthcare providers may need to be more proactive when treating diabetes as well as cancer. Our research suggests that women with diabetes who are diagnosed with breast cancer may get less-effective treatment because providers may be concerned about increased risks for side effects from chemotherapy or radiation treatments that result from their metabolic condition. Patients may also be more likely to be hospitalized, get infections, or become anemic, all of which are factors that complicate care. It should be noted that patients with diabetes may be at greater risk of chemotherapy-related toxicity, which may explain some of the rationale for being given less-aggressive treatments.

Research Needed on Pathophysiologic Interactions

The findings from our analysis indicate that we need more clinical studies that investigate the pathophysiologic interactions between diabetes and breast cancer. Our research does not assess a causal relationship between diabetes and mortality outcomes in breast cancer. Determining whether improvements in diabetes care can reduce mortality in patients with breast cancer is important. Researchers should also try to determine if increased insulin production in type 2 diabetes contributes to worse outcomes among these patients. A few smaller studies have suggested that some diabetes drugs may be associated with worse outcomes for cancer patients while others may actually improve survival. Finding the answers to these questions is paramount to optimizing outcomes for this patient group.


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